System for automated production of spark plugs

ABSTRACT

A system for automated production of spark plugs, which comprises a first station for the production of insulators, a second station for the assembly of the central component of the spark plug, and a final assembly station; each station operates, at least partially, in continuous kinematic motion, and the transfer means between the stations comprises storage means. The system also comprises means for servo-control and synchronization of the stations, the parts, before their final assembly, being transferred in vehicles belonging to each station or part of a station.

United States Patent 1 Goutard [4 1 Nov. 26, 1974 SYSTEM FOR AUTOMATED PRODUCTION OF SPARK PLUGS [75] Inventor: Rene Michel Goutard, Verrieres Le Buisson, France [73] Assignee: Automatisme & Technique, Arcueil (Val de Marne), France [22] Filed: Sept, 20, 1973 [2]] Appl. No.: 398,927 no] Foreign Application Priority Data Sept.22 1972 France ..72.33739 [52] U.S. Cl 29/25.19, 29/200 A, 29/430 [51] Int. Cl. H0lj 9/48 [58] Field of Search 29/25.l9, 25.2, 25.12,

29/429, 430, 200 A, 203 D, 208 D; 198/19 [56] References Cited UNITED STATES PATENTS Christie et al. 29 25.19

Primary ExaminerRoy Lake Assistant ExaminerJames W. Davie Attorney, Agent, or FirmKinzer, Plyer, Dorn & McEachran [5 7] ABSTRACT A system for automated production of spark plugs, which comprises a first station for the production of insulators, a second station for the assembly of the central component of the spark plug, and a final assembly station; each station operates, at least partially, in continuous kinematic motion, and the transfer means betweenthe stations comprises storage means, The system also comprises means for servo-control and synchronization of the stations, the parts, before their final assembly, being transferred in vehicles belonging to each station or part of a station.

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SYSTEM FOR AUTOMATED PRODUCTION or SPARK PLUGS The present invention relates to a system for the automated production of spark plugs for internal combustion engines.

Present systems for mass production of spark plugs require a number of machines operating on a batch basis. Each machine produces or assembles the constituent parts of a spark plug; usually, a sub-assembly of part is. first produced, then stored, and subsequently brought to another machine where additional operations are carried out, also on a batch basis. These systems, of very varied types, all have the disadvantage of giving relatively low production rates, being complicated, and requiring a relatively large amount of labor, as there are many handling operations between the machining and assembly machines.

for automated production of spark plugs at a high rate,

which can be adapted to the production of a wide variety of types of spark plug by simple additions to or modifications of the constituent parts.

To this end, the invention relates to a system for the automated production of spark plugs, characterised in that it comprises a first station for the production of insulators, a second station for the assembly of the central component of the spark plug, and a final assembly station, each station operating at least partially in continuous kinematic motion. The transfer means between the stations comprises storage means; the system also comprises means for servo-control and synchronization of the stations, the parts, before their final assembly,

being transferred in vehicles belonging to each station or part of station.

- Under the invention, the system for automated production of spark plugs combines the advantages of a series of production stations operating in continuous motion, at a high production rate, with the avoidance of the disadvantages of a too rigid and complicated construction, by virtue of the transfer means between the stations. This transfer means comprises storage and synchronization means, allowing compensation for changes in the relative operating rates of the stations without interrupting operation of the overall system.

is very much longer than that of the operations that precede it, the insulators are passed in parallel lines through several curing tunnels in order to obtain a sufficient output rate. Moreover, because the sintering machine in separate, special vehicles especially suited to heat treatment can be used in it; these vehicles are not necessarily identical with the vehicles used in the compacting and machining apparatus.

The completed insulators are transferred to a central component assembly station, in which the internal conductive components are assembled in each insulator and cemented in place. At the next and final station, the conductive holder is mounted on each central component, together with any required mounted gaskets and the like, finishing the complete spark plug manufacturing operation. The transport between the operating station allows for some differential in production rates without requiring system shutdown.

The system of .the invention, some principal characteristics of which are enumerated above, produces spark plugs automatically at a high rate, but is not limited to any one type of spark plug, and can be adapted to different types very simply by changing or moving a The system of the invention starts with a rotary insulator compacting mechanism, which produces a series of dense, compacted insulator blanks. These insulator blanks are transferred to an insulator machining drum that includes a mill. The forward machining speed of the mill is adjusted uniformly or proportionally to the mass of the matter removed, by means of a cam also used to compensate for wear of the mill. The machining drum is enclosed so that dust and other machining byproducts are controlled and contained. These byproducts are recovered for use in the fabrication of new blanks, for which purpose they can be returned to the hopper ofthe initial compacting drum. The mill of the machining drum can be dismantled rapidly to allow for effective maintenance operations conducted outside the machine.

The system utilizes a sintering machine which is separate from the compacting and machining apparatus; consequently, heat from the sintering machine does not adversely affect the compacting and machining operations. Because the duration of the sintering operation working unit or a working drum. Since the parts, and particularly the insulators, are transported in vehicles, they are not subjected to wear or shock, which considerably reduces the number of plugs that are rejected. Another advantage of this method resides in the fact that since the insulator is not subjected to wear, there is no formation of abrasive dusts, which can cause rapid wear of the components of the machines and the systern.

The present system will be described in greater detail with the aid of one embodiment of the invention, represented schematically, by way of non-limitative example, in the accompanying drawings in which:

FIG. 1 is a detailed view of a conventional spark plug, which can be produced by a system constructed in accordance with the invention;

FIG. 2 is a detailed elevational view of the central component of the spark plug of FIG. 1;

Y FIG. 3 is a schematic diagram of the whole of the system according to the invention;

FIG. 4 is an axial half cross-section of the insulator compacting drum;

FIG. 4A shows a detail of the compacting drum in the mold closure area;

FIGS. 48, 4c, 4D ShOW schematically the three stages of the operation of the compacting drum;

FIG. 5 is a detailed view of the axial cross-section of the insulator machining drum;

FIGS. 5A and 5B show the insulator being machined on the drum of FIG. 5; v

FIG. 6 is a plan view of the whole of the central com ponent assembly station;

FIGS6A through 6H show the various stages of the assembly of the central component of a spark plug at the station of FIG. 6;

FIG. 7 is a schematic plan view of the final assembly station;

FIGS. 7A through 7N show the various stages of the work in the final assembly station of FIG. 7;

FIG. 8 is an axial section of the insulatorintroducing drum;

FIGS. 8A and 8B are horizontal cross-sections taken approximately along lines VIIIaVIIIa and VIIIb-- VIIb in FIG. 8;

FIG. 9 is an axial section of a detail of a marking drum;

FIG. 10 is a right hand, half section of an enamelling drum utilized in the system of the invention;

FIG. 11 is an axial sectionv of an electrodeintroducing drum;

FIG. 11A is a detail sectional view taken approximately along line XIA in FIG. 11;

FIG. 11B is a horizontal section taken approximately aling line XIBXIB in FIG. 11;

FIG. 11C is a detailed view of the end piece of the electrode feed rails;

FIG. 11D is a plan view of the drum of FIG. 11;

FIG. 12 is an axial half-section of a cementintroducing drum;

FIG. 12A is a simplified horizontal section taken approximately along the plane XIIA in FIG. 12;

FIG. 13 is a partial axial section of a connecting rodintroducing drum;

FIG. 13A is a detailed horizontal section taken approximately along the plane XIIIA in FIG. 13;

FIG. 14 is a detailed axial sectional view of a'drum for positioning the lower gasket;

FIG. 14A is a plan view of a gasket-arrival slide piece;

The system comprises an insulator-production station 1, constituted, in general, by an insulator compressing and machining machine 11 and a sintering machine 12. These two machines operate in continuous kinematic motion and are interconnected through a series of transfer drums.

FIG. 148 shows the successive stages in the introduc- I tion of the gasket;

FIG. 15 is an axial cross-section of an assembly compacting drum;

FIG. 16 is a detailed axial section ofa crimping drum;

FIG. 17 is a detailed view of the axial section of a connecting-nut screwing drum;

FIG. 17A shows the axial cross-section of the area in which the nut screwing drum is associated with the transfer drum that feeds it;

FIG. 178 shows a plan view of the same area as that in FIG. 17A;

FIG. 18 is a detailed axial cross-section of a sealing control drum.

The system of the invention provides fully automated manufacture of spark plugs for internal combustion engines. In general, and without the system being limited to any specific type of spark plug, the system may be utilized in manufacturing a conventional spark plug (FIG. 1) which comprises a central subassembly a. consisting (FIG. 2) of an insulator b, rotationally symmetrical, and having an axial opening into which an electrical connection rod 0 extends. The rod 0 is connected to an electrode d. The cement e forms this electrical connection and alsoimmobilizes the rod 0 and seals the central subassembly or component a. The central component a is mounted in a metal holder f that is adapted to be screwed into the cylinder head of an engine. A seal between the holder f and the central component a is obtained at the upper part of the spark plug by means of an upper gasket h, pressed against the central component a by the crimp I. This seal is reinforced by a lower gasket k. In use of the spark plug, the holder f is screwed, so as to effect a seal, into the cylinder head of an engine, by means of a cylinder head gasket 1'. Lastly, a nut g is threaded onto the free end of the rod 0.

FIG. 3 is a schematic diagram of the whole of a system or machine for the production of spark plugs similar to the plug described above in relation to FIGS. 1 and 2.

The compressing and machining machine 11 comprises a compressing drum 111 which forms a stable insulator blank from a predetermined quantity of inorganic powder. The machining drum 112 machines this blank in order to give it a form approximating that of the final insulator b. (FIGS. 1 and 2). The machine 11 (FIG. 3) comprises a number of transfer drums 113, which transfer the blanks between the drums Ill and 112, as well as returning the vehicles receiving these blanks.

The insulator-production station 1 comprises, in addition, a sintering machine 12 which is supplied by a loading and transfer device 121, which brings the insulators into a sintering or curing tunnel I22 .and then into a cooling area 123. Four curing tunnels 122 are shown in FIG. 3; a larger or smaller number may be provided, depending on the production rate of the system and other related factors.

The loading device 121 is an endless conveyor comprising a vehicle-loading component 1211 at the outlet point of the compressing and machining machine 11, a component 1212 for distributing the vehicles carrying the insulators to the curing or sintering lines passing through the respective curing tunnels 122. On emerging from the cooling area 123, there is a combining component 1212 similar to the loading component 1212 but operating in the opposite manner. This combining component 1212' combines the four lines of vehicles into a single line.

Lastly, an unloading componnet 1211' enables the sintered insulators b to be separated from the transfer vehicles which are brought back to the loading component 1210.

The insulators I) thus manufactured in station I pass into a central component-assembly station 2. This station 2 comprises a central component-assembly machine 21 and curing station 22. The central component-assembly machine 21 comprises a certain number of working drums.

In the present case, the machine 21, shown in further detail in FIG. 6, comprises an insulator-introducing unit with a number of drums 210 and a distributor 219, in which the insulators b are placed in position in vehicles for transfer to the machine 21, a marking drum 211, where identification indicia and other marks are printed on the insulator, and a flaming drum 212 which dries the marking ink and pre-heats the insulator before its passage into an enamelling drum 213 which coats the insulator with enamel.

This assembly machine 21 also comprises an electrode-introducing unit, including a drum 214 and an electrode distributor 219, followed by proportioning and compacting drums 215, 215' for the cement, and a unit 216 for introducing the rods 0 comprising a drum 216 and a distributor 219". Following this, the assembled part is checked in an assembly control drum 217. If the result of the check is satisfactory, the vehicle and the assembled central component a pass to the vehicle changing drum 218, in which the central component a which has just been obtained, leaves the vehicle of the machine 21 and is brought into a heat-treatment vehicle V (FIG. 6H).

The machine 21 (FIG. 6) comprises a number of distributors such as the insulator distributor 219, the electrode distributor 219 and the connecting rod distributor 219". These distributors, of known construction, are connected to the corresponding drums 210, 214, 216.

The check that is made in the drum 217 consists in checking the level of the head of the rod c. Thus, if any of the constituent components are defective or are not of the required size, the level required is not reached and the vehicle is diverted from its normal trajectory and ejected from the system.

The change of vehicle effected at the drum 218 is necessary because the central component a is to be cured. For, in the assembly machine 21, the vehicles are intended simply to support the insulator b during the assembly of the component a. The assembly vehicles are subjected only to mechanical stresses. However, during heat treatment, the vehicles V must be able to withstand temperatures of above 1,000 C but do not have to withstand any further great mechanical stresses. 7

The assembly vehicles of the machine 21 are recovered by the vehicle changing drum 218 and brought back to the introducing drum 210.

The heat-treatment vehicles V enter the assembly station 2 by passing through a synchronization device such as a helicoidal-screw which brings them to the operating speed of the station 3 (FIG. 3). The empty vehicles V are brought back to the machine 21, if necessary, passing through a storage device such as the turning tables 225. On entering the machine 21, the vehicles are again synchronized in accordance with the speed of the machine 21.

These operations take place in various drums 211 tp 217 and are shown schematically in FIGS. 6A through 6H.

FIG. 6A shows the insulator b being marked, FIG. 6B shows the insulator b being flamed or pre heated, FIG. 6C shows the insulator b being enamelled, FIG. 6D shows the electrode d being introduced, FIG. 6E shows the cement e being introduced and compacted, and FIG. 6F shows the rod 0 being introduced. FIG. 6G shows the assembled but uncured central component a being checked and FIG. 6H shows the vehicles being changed, that is, the assembled central component a being transferred from the vehicle of the machine 21 to the heat-treatment vehicle V.

On leaving the assembly machine 21, the assembled central component a with its vehicle V is conveyed to the curing station 22 (FIG. 3). This curing station 22 consists of a transfer device 221 which conveys the untion 3, having passed through the storage devices 224. e

The pressing drum 223 cools the parts leaving'the curing station 22 by means of forced convection and a given mechanical pressure. As an example, the pressing operation is carried out for a period of seconds, which corresponds to the setting time of the cement e under the heating conditions of the example. On leaving the drum 223 the parts are conveyed to the final as sembly station 3. Dynamic storage devices 224 are provided between the assembly station 2 and the station 3 in order to compensate for any lack of synchronization between the station 2 and the station 3. These devices 224, for example, may comprise turning tables arranged in series. The reserves which they can carry are variable. In the particular case where the reserve is nil, the parts pass directly through the storage devices 224.

When the stations 2 and 3 are synchronized, it is advantageous to have the devices 224 half filled. If the station 2 stops operating, the station 3 can continue to operate until the reserves are exhausted. If the station 3 stops operating, station 2 can continue operating until the storage devices 224 have been filled. This allows limited shutdowns of either station 2 or station 3 without interruption of overall system operation.

Lastly, it is possible to servo-control the system so that the operating rate of the stations 2 and 3 is a function of the rate at which the storage devices 224 are filled.

The divider component 221 divides the single line of vehicles V coming from the assembly machine 21 into a certain number of parallel lines, for example, three, which pass through the respective tunnels 222 of the passage oven 22. On leaving these tunnels, a combining component 221, similar to the divider, but operating in the opposite manner, recombines the several lines again into a single line.-

In the final assembly station 3, each central component a is separated from its heat-treatment vehicle V and the vehicle is returned at the vehicle-changing drum 218 of the assembly machine 21.

The final assembly station 3 assembles the central component a into the holder f, interposing the gaskets h, i, k, and screwing the nut g (FIGS. 7A-N).

The assembly station 3 (FIG. 7) comprises a unit for introducing the holder f including a drum 301 and a drum 302 for positioning the lower gasket k. Following this, a drum 303 is provided for inserting the central component a into the holder f provided with a lower gasket k. This partial assembly is controlled in a control drum 304 and the part then passes into the unit which positions the upper gasket h, comprising the drum 305.

A drum 306 in the compacting unit places the whole into position and a cold crimping drum 307. in the crimping unit turns over the upper lip of the holder f, in order to hold the upper gasket h.

A heating drum 308 heats the holder and a drum 309 hot crimps the assembly. The connecting nut g is screwed onto the part that has been made in the screwing drum 310 of the unit for distributing the nuts g. The spark plug is then finished. A drum 311 adjusts the electrode and a drum 312 checks the seal of the spark 

1. A system for automated production of spark plugs comprising: a first insulator-production station, comprising insulator compressing means for forming insulators of compressed particulate dielectric material, machining means for shaping insulators and sintering means for sintering the insulators; first transfer means for transferring the sintered insulators to a second station; a second component-assembly station for receiving the sintered insulators from the first station and assembling central spark plug components, comprising means for inserting at least one electrically conductive element into each insulator, together with a heat-curable cement, and curing means for subjecting the assembled insulators, conductive elements, and cement to heat to cure the cement and form complete central spark plug components; second transfer means for transferring the central components to a third station; and a third final assembly station for receiving the central components from the second station and assembling completed spark plugs, comprising means for mounting each central component in a conductive holder; each of the first, second, and third stations operating at least partially in continuous kinematic motion; at least one of the transfer means including storage means to compensate for limited differences in production rates in the two stations it interconnects; and the parts of the spark plugs, prior to final assembly, being transferred within each station in vehicles which remain in the station and are not transferred to any other station.
 2. A system according to claim 1, in which the insulator-production station comprises a compressing and machining machine for receiving a dielectric ceramic powder of which the insulators are composed, compressing the powder to form insulator blanks, and machining each blank into the shape desired for an insulator.
 3. A system according to claim 2, in which the compressing and machining machine comprises a compression drum receiving the powder for the insulator and compressing it into the insulator blanks, a machining drum receiving the insulator blanks and machining each blank into the finished form of an insulator, and a series of transfer drums linking the compression drum to the machining drum for circulating a multiplicity of vehicles between the compression drum and the machining drum, each vehicle carrying an insulator blank from the compression drum to the machining drum and returning empty to the compression drum.
 4. A system according to claim 3, in which the compression drum comprises a fixed hopper for storing sufficient powder to form a multiplicity of insulator blanks, a rotary tray revolving with the drum, a series of adjustable proportioners each comprising a mold having deformable walls, a needle insertable into each mold to form an internal cavity in an insulator blank formed in the mold, an isostatic pressure generator communicating with the deformable walls of the molds to exert a given isostatic pressure, corresponding to the required pressure in the mold, a rotary transfer tray having a series of recesses located above the tray carrying the molds, the transfer tray having a series of recesses which carry individual vehicles for transporting molded blanks out of the compression drum, the succession of operations of the drum comprising, in sequence, the filling of a mold by its proportioner, the introduction of the needle into the mold, compression molding of the blanks, and transfer of the blank to a vehicle in the transfer tray, all of the operations being controlled and synchronized by the rotation of the drum.
 5. A system according to claim 3, in which the machining drum comprises a rotary tray provided with a series of recesses to receive the insulator blanks, carried in individual vehicles, a machining mill with a contour which is complementary to the contour to be given to the insulator blank, a machining tray, integral with but axially displaced from the tray carrying the vehicles, a series of support needles, one for each recess and each movable, with respect to the mill, between a position coaxial with the axis of the corresponding recess, for removing a blank from and returning the blank to its vehicle, the movement of the needles with respect to the mill being controlled by the rotation of the drum, thereby insuring that the milling operation is carried out progressively, and driving means for rotating the blank about its axis, during the milling operation, all the movements being controlled by the rotation of the drum, while the mill, which is coaxial with the drum, rotates at a speed which is different from that of the drum.
 6. A system according to claim 2, in which the sintering means comprises at least one curing tunnel through which the machined insulators pass, the curing tunnel being followed by at least one cooling area and a sintering transfer means which passes the insulators through the curing tunnel and the cooling area.
 7. A system according to claim 6, in which the sintering transfer means comprises a series of refractory vehicles each adapted to carry one insulator, an endless conveyor which carries the refractory vehicles through a plurality of curing tunnels and the cooling area, a loading drum, and an unloading drum, the endless conveyor cooperating with the unloading drum to effect the reverse operation of the loading drum at the exit of the cooling area, the curing tunnels being preceded by a distributor and the cooling area being followed by a line combiner which respectively divides the line of refractory vehicles carrying the insulators into a predetermined number of parallel lines passing through the curing tunnels and the cooling area, these parallel lines being re-combined into a single line on emerging from the cooling area.
 8. A system according to claim 1, in which the component-assembly station comprises a central component assembly machine for performing the insertion operations, and in which the assembled components are exchanged between the assembly machine and the curing means by a transfer made in continuous kinematic motion.
 9. A system according to claim 8, in which the central component assembly machine comprises a unit for introducing the insulators, a rotary unit for marking and enamelling, a unit for introducing an electrode into each insulator, a unit for supplying the cement and compacting it into the insulator around the electrode, and a unit for introducing an electrical connection rod into each insulator in engagement with the cement, each unit comprising at least one drum, and the units exchanging the assembled parts in continuous kinematic motion.
 10. A system according to claim 9, in which the unit for introducing the insulators comprises a plurality of distributor tubes through which the insulators pass one aftEr the other, each tube terminating above an introducing drum, two separators revolving synchronously with the introducing drums and at each turn distributing an insulator above a relevant recess in the drum which carries a vehicle ready to receive an insulator, each introducing drum depositing an insulator in only one vehicle out of a predetermined number K, where K is the total number of introducing drums in series.
 11. A system according to claim 9, in which the marking unit includes a marking drum which comprises a marking tray having a series of recesses for receiving vehicles each carrying one insulator, a printing drum, a lower tool for releasing each insulator from its vehicle and engaging the insulator in an upper tool, and a needle engageable in a central aperture in the insulator, the accessory formed by the upper tool and the lower tool being driven rotatively by a marking pad carried by the printing drum, the axis of which is fixed and occupies a satellite position with respect to the axis of rotation of the marking tray, the printing drum carrying the printing pads on its periphery of its revolving tray and rotating synchronously with the marking tray so as to bring each insulator and each marking pad into contact when the marking drum is rotating, the printing operation being carried out by contact without substantial friction, and the insulator being returned to its vehicle after the printing operation.
 12. A system according to claim 9, and further comprising an enamelling drum including an enamelling tray having a series of recesses each receiving a vehicle carrying an insulator, a lower tool, and a plurality of enamelling nozzles, the lower tool releasing the insulator from the vehicle and supporting the insulator for an enamelling operation, the lower tool being driven rotatively with respect to the enamelling tray that carries it, the enamelling nozzles being integral with the enamelling tray opposite each insulator in the free position and a pneumatic distributor revolving with the enamelling drum and pumping varnish into a storage vessel, the insulator being returned to its vehicle upon completion of the enamelling operation.
 13. A system according to claim 9, in which the unit for introducing electrodes into the insulators comprises a distributor with guide rails bringing the electrodes to a level adjacent the axis of an electrode introducing drum, the electrode introducing drum comprising an insertion tray having a series of recesses for receiving a series of vehicles each carrying an insulator, a guide tray having radial corridors, coaxial with and rotatable with the insertion tray, each radial corridor starting at the center of the insertion tray and ending on the periphery at an aperture of a size greater than the greatest radial dimension of the electrode, and coaxial with each vehicle in a recess, the guide tray receiving the electrodes separately, by gravity, through a hub having a cavity cooperating with the forward end of the guide rails, and a fixed helix for guiding the heads of the electrodes to move them from the axis of the drum toward its periphery above the aperture of the respective radial corridor where the transfer of the electrode into the insulator is effected.
 14. A system according to claim 9, in which the unit for introducing the cement comprises a cement storage hopper mounted for rotation with a cement dispensation drum, the bottom of the hopper having a series of supply orifices corresponding to a series of recesses in the drum, a non-rotating scraper engaging the bottom of the hopper, at the level of the orifices, to mask the orifices during a part rotational movement, and means for dispensing and packing cement comprising a piston movable in tralsation, partly introducing itself into each hopper orifice to define with the upper surface and the lateral surface of the orifice a volume Q corresponding to the amount of cement to be dispensed, the return movement of the piston dispensing the quantity Q of ceMent into the central aperture of each insulator, the piston also carrying a needle which, after the introduction of the cement into the insulator, is actuated to pack the cement, the movement of the piston and of the needle which it carries being controlled by fixed cams, during the rotation of the drum.
 15. A system according to claim 1, in which the final assembly station comprises a unit for introducing a series of conductive holders and inserting into each holder a lower gasket, a drum for inserting an assembled central component into each holder, a distributing unit for inserting an upper gasket into each holder, a unit for compacting and crimping each holder against the associated central component, a unit for mounting a connection nut on each central component, electrode adjustment and checking drums, a drum for placing a cylinder head gasket into position on each holder, a drum for testing dielectrically the whole of the operations and transfers effected in continuous kinematic motion, and each of the units comprising at least one drum, with all of the drums being mounted interchangeably.
 16. A system according to claim 15, in which the holder introducing unit comprises a holder distributor feeding a first drum for introducing the holders and a distributor of lower gaskets, feeding a second drum for receiving the holders from the first drum, for placing a lower gasket into position on each holder.
 17. A system according to claim 15, in which the compacting and crimping unit comprises a compacting drum which receives a series of assemblies each comprising a holder, a lower gasket, a central component and an upper gasket, and which compacts this assembly, a cold crimping drum for subsequently crimping the holder to the central component, a heating drum for heating the cold-crimped holder, and a hot crimping drum for subsequently crimping the heated holder.
 18. A system according to claim 17, in which the compacting drum comprises a tray having a series of recesses for receiving the assemblies, a lower tool supporting each assembly by the holder during the compacting operation, and an upper tool which comes to bear on the upper gasket of the assembly with a calibrated force, all these operations being controlled by fixed cams, during the rotation of the compacting drum.
 19. A system according to claim 17, in which the cold and hot crimping drums each comprise a rotary tray having a series of recesses for receiving the assemblies to be crimped, a lower tool for supporting the holder of the assembly during the crimping operation, and an upper tool exerting a calibrated force on the edge of the holder to crimp it, the various movements being controlled by fixed cams, during rotation of the drum.
 20. A system according to claim 15, in which the unit for distributing the electrical connection nuts comprises a distributor which orients the nuts and a device for bringing the nuts above a distribution and screwing drum comprising movable components which seize the nuts in flight and make them slide along a ramp and fall onto the threaded end of the connecting rod, by cooperating with a guide needle constituting an upper tool, the guide needle entering the upper orifice of the nut and, when the latter is in position, coming onto the threaded end and tightening the nut by rotation.
 21. A system according to claim 15, in which the unit for placing each of the lower, upper and cylinder head gaskets into position, comprises a central rotary tray having a series of recesses carrying the assemblies which are to receive the gaskets, a guide ramp bringing the gaskets in a line following the periphery of the circular course of the assemblies, an upper tool, including a needle, corresponding to each recess, for catching each gasket in flight, driving the gasket along the ramp and dropping the gasket into position on the assembly.
 22. A system according to claim 15, including a seal test drum comprising a vertically movable pusher, which pushes each spark plug into a cavity in which a predetermined pressure is produced by passing compressed air into the cavity through a check valve, the whole being connected to a pressure multiplier actuated by the movement of the seal test drum, any seal defect of the spark plug being detected by a manometer which causes the defective spark plug to be ejected. 